If you have an electronic device, you most probably can read books in it. Computers, tablets, smartphones and specific readers, all of them may be used to enjoy your reading. For that purpose, you will need hardware and software.
There are specific ebook readers in different formats: ePUB, Mobi/AZW/KF8, PDF, TXT. They may even reproduce MP3 audio files. These devices do not need additional software, because they are ready for their purpose.
Smartphones may load applications (apps) to manage different ebook formats. Even the main ebook distributors have their own applications for reading ebooks in smartphones.
Like their cousins the smartphones, tablets may load apps to manage ebooks. It does not matter if your tablet is an iPad or an Android, your app store will provide you with software to read ebooks. Just search ebook and select the software of your choice.
Mac OS/X, Linux, even Windows, they all have applications to read ebooks in different formats. You can use Apple's App Store, your package manager in Linux or application download sites for Windows.
Different ebook formats have been used in different times, with different levels of success. Nowadays, two are the most used ebook formats:
Amazon adapted the Mobi format, which evolved as an specialisation of Palm's PRC format, adding its own features. The result is the AZW format, which has recently evolved into the KF8 format (Kindle Format version 8).
For the enthusiasts of open software and formats, ePUB is their choice. The most extended version is still ePUB version 2, while version 3 is gaining. This is an adaptation of HTML 5 to ebooks, with many more multimedia and interactive capabilities.
You may find useful to find what software allows ebook reading for several formats and operating systems:
All distributions include ePub readers.